1. Field of the Invention
The present invention relates generally to an apparatus and a method for packetizing a coded bitstream of digital data in accordance with a transport protocol. More particularly, it relates to an apparatus and a method for packetizing the bitstreams wherein time information is generated in accordance with a specification of the protocol, a header including the time information is generated, and a packet including the time information in accordance with the protocol is generated with adding the header to every predetermined unit of the bitstreams.
2. Description of Related Art
Many researches for digital broadcasting utilizing an MPEG4 stream defined by the Moving Picture Experts Group, a working group of ISO, as ISO/IEC 14496 are going on to find an alternative to an MPEG2-stream (ISO/IEC 13818), which has been conventionally used for the digital broadcasting.
Syntax of a stream of MPEG4 Visual Object Sequence defined as ISO/IEC 14496-2 is shown in FIGS. 1 and 2. At the top of the hierarchy as shown in FIG. 1 is the Visual Object Sequence. The Visual Object Sequence includes mostly Profile and Level indications of the stream. Each Visual Object included in the Visual Object Sequence describes a type of objects that are multiplexed on the stream. Thus, this allows the MPEG4 to define a plurality of visual objects such as still-frame video image objects, face objects, and video objects.
The case that the video objects are multiplexed on the stream will be described. Information, “visual_object_type (4): 0×01” described in the Visual Object indicates that the type of Visual Object is video object. If the type of Visual Object is video object and the Video Objects are multiplexed, the Visual Object includes Video Object Layer. The Video Object Layer includes a type of Video Object, a bit rate of the stream, a size of a buffer of the receiver side, occupancy of data to be stored in the buffer of the receiver side up to a start of the decoding, and a frame rate.
Herein, the information of 30 bits, “first_half_bit_rate (15)” and “latter_half_vbv_bit_rate (15)”, described in the Video Object Layer indicates the bit rate of the stream. The information of 18 bits, “first_half_vbv_buffer_size (15)”0 and “latter_half_vbv_buffer_size (3)”, described in the Video Object Layer indicates a size of the buffer of receiver side. The information of 22 bits, “first_half_vbv_occupancy (11)” and “latter_half_vbv_occupancy (11)”, described in the Video Object Layer indicates the occupancy of the data to be stored in the receiver side up to a start of the decoding. The information, “vop_time_increment_resolution (16)” and “fixed_vop_timeincrement (1-16)”, contains information to get the frame rate. Although the information from “first_half_bit_rate (15)” to “latter—half_vbv_occupancy (11)” as described above exists when “vbv_parameters (1)” are set to 0x1, it does not exist when they are set to 0x0 where “0x” indicates hexadecimal digit.
The Video Object Layer may Include Group of Video Object Plane. The Group may be excluded in compliance with a stream. The Group includes Time code. It also includes Video Object Plane (hereinafter called VOP). The VOP corresponds to a frame of picture in the video images. Here, it includes VOP coding type and an order of reproduction. The information, “vop_coding_type (2)” described in the VOP indicates I-picture, P-picture or B-picture. The information, “modulo_time_base” described in the VOP indicates how many seconds it takes for a picture to occur after I-picture. The information, “vop_time_increment (1˜16)” described in the VOP indicates how order the picture should occur, namely, the order of reproduction thereof. The VOP includes the bitstreams each indicating internal information of VOP following the above information.
Many researches for transporting the bitstreams each having the above syntax on the Internet and/or broadcasting waves have been done.
MPEG4 stream fails to define transport stream (hereinafter called TS) and packetized elementary stream (hereinafter culled PES), which are available in the transport thereof. Thus, although a user can freely set TS End PES, he or she is required to alter their stream structure according to the transport protocol thereof.
In ISO 13818-1/FDAM7 (ISO/IEC JTC1/SC29/WG11 N3050), standardization in ease of using MPEG2-TS goes on whereas implementing method, namely, translation method that the MPEG4 stream is translated into an MPEG2 packetized elementary stream (hereinafter. called MPEG2-PES) packet has not been determined.
Alternatively, MPEG4 Visual Object Sequence (ISO/IEC 14496-2) fails to multiplex time information such as elementary stream clock reference (hereinafter called ESCR), decoding time stamp (hereinafter called DTS), presentation time stamp (hereinafter called PTS), which is necessary for the synchronization in a packet. Thus, it is necessary to transport the MPEG4 Visual Object Sequence with adding the time information in order to attain the synchronization.
Japanese Patent Publication, JP-H11-98193-A, discloses a translation of MPEG4 stream into MPEG2-PES packet. It, however, discloses no particular way of translation.
It is an object of the present invention to present an apparatus and a method capable of obtaining a packet including the time information in accordance with the transport protocol.